Prusiks

[paulyb]

Hi all,

I'm getting gear together for a drt split tail system and had some questions about the prusik. I have read a lot of different information about what the prusik diameter should be relative to the climbing rope, but I can't figure out exactly what I should get. My climbing rope will be a 16 strand, 1/2" rope. So my question is:
As far as deciding on a prusik diameter, does it matter what friction hitch I plan on using (I am thinking a schwabisch)? Can I just use the same diameter as my climbing rope? This is how it's done with a closed system, so it seems like it would work, but then would I be limited to just using a blake's or taut line hitch? When learning about hitches, a lot of people don't tell you the diameter of their lines, so I'm a little lost. Ultimately I want to get a prusik that is safe and not limited in which hitches I can use.

Thank you for any help.

 

[Rtodd79]

I'm definitely an amateur however I do know that your prusik needs to be smaller diameter than your climbing rope. I use a 10mm Armor prusik rope for mine.

Sent from my SM-G955U using Tapatalk

 

[Bango Skank]

I’m not sure if the schwabisch will work with same diameter. Try it out very very close to the ground. The termination knots for the hitch cord are probably gonna be pretty bulky though.

I’ve always heard/ read that the hitch cord should be around 3mm smaller diameter than the climbing rope, so 10mm or 3/8” cord on 13mm or 1/2” rope, and 8mm or 5/16” cord on 11mm or 7/16” rope, but I used 5/16” UltraTech on 1/2” XTC-16 for a couple years. Worked just fine with a VT. I think it was 3 wraps, 2 braids on the VT.

I still use 5/16” UltraTech now, but with 11.7mm rope. Nice stuff, it lasts forever, takes a beating, holds up well to friction and heat generated from fast SRT descents with a RopeWrench.

 

[Harmon]

I always thought that for a standard alpine prussik as well as things like the valdotain (?) tress (VT) or distel hitch the prussic cord should be 75% of the rope diameter. For a split tail which is a different animal (ie, not the same as a prussik) where you use blakes or taut line hitch you use the same diameter as the rope.

 

[TheTreeSpyder]

The number of support 'legs' placing load between Friction Hitches(FH) and host line; determines if mechanically need smaller diameter in matching rope materials.
>>smaller/tighter/more rigid load bearing FH cord diameter against host is needed if connects 2 legs of FH to saddle.
>>want the host imposed on to be softer (or equal) than FH imposing onto/into host.
.
i think/visualize in terms of an active/persisting load is 'imposed' onto a dormant, passive/but responding rope (as with any other dormant support structure).
Another fave term is 'displacement', an extending height displaces against space above, just as antagonistic forces displace against each other in this.
.
FH then must impose on the host line. To be mechanically positive/ not maybe-baby land;
>>this logically takes tension x rigidity to be greater or matching in the Friction Hitch over the host.
BUT if weigh 100#, 2 leg FH places 50# on each support leg, to then grab a host line that is receiving full 100# tension.
>>read as: 50#tension trying to be more rigid/displace/impose against 100#host(matching materials and diameters)!!??
>>In Matching materials and diameters the host would be more rigidly 'bloated' with force, against being imposed on than the FH imposing with half that force.
>>we drop the diameter of the 2 leg FH/cord to 50-75% of the host to give FH advantage to concentrate force to smaller footprint, and thus rigidity against the host.
>>we may even choose stiffer cord material/construction than host line to aid in gaining greater rigidity value than the host.
Thus if this or that FH can be same diameter as host depends on:
>>if 'open' 1 leg of support can be more matching diameters but not greater
>>if 'closed' (circle) of 2 legs support (or any load dividing multiple) then look to have smaller cord diameter
And more rigidity in cord/FH helps to impose against host also; don't want host to be more rigid than cord; that would reduce/guard firmer against FH imposing on host.
oldie but goldie:

To an age old question, i think that FH is properly termed a Hitch (termination) not Bend(coupling) as a node deformity in otherwise continuous line.
>>for knots/rope work are/is ruled by arcs(mostly in 180 degree parts in all but Round Binding)
>>and the host line would have to make arcs to FH to be a Bend then properly. Can be used as a Bend, but terminology of Hitch is correct by that measure.
Only the FH makes arcs to host, but not host to FH, so must be Hitch.
.
By contrast if use a Constrictor/Bag/Ground Line (family) as a Hitch it does load differently than if used for Round Binding;
>>Each of these will degrade tension around the host, and then compound tension into host at arc apexes as a Hitch
>>but in Round Binding the same form has no degrading tension around host(before nips), nor compounding into host
>>naming therefore could be more transitory to define forces etc.; but stick with convention to be understood.
But forces in FH to host more definitively a Hitch by this measure.

 

[hosocat]

I always thought that for a standard alpine prussik as well as things like the valdotain (?) tress (VT) or distel hitch the prussic cord should be 75% of the rope diameter. For a split tail which is a different animal (ie, not the same as a prussik) where you use blakes or taut line hitch you use the same diameter as the rope.

Although, for quite a few climbs I used a10mm ocean polyester split tail Blake's hitch on my 1\2 inch Arbor master 16 strand and it seemed to do fine.

 

[TheTreeSpyder]

'Agent Smith' writes and collects many fine rope articles and being a climber many of them on Friction Hitches. @ Professional Association of Climbing Instructors in Australia(link). 20-23, 29, some in the 40's to; but all good stuff.
.
'Life on a Line' is very good also, a tour thru many rope mechanix including Friction Hitches courtesy of Dr.Merchant(link).
.
All these were very important to me personally building understanding.
.
More data mining for the gold in archives of the Nylon Highway(link)

Plus really love the name, spirit and honesty of the 'Life on a Line', and 'Nylon Highway' (a road I learned many things on) as titles !

 

[paulyb]

Thank you all very much for the resources and knowledge! I will go for a slightly thinner prusik than my main line!

 

[Howard Justice]

I always thought that for a standard alpine prussik as well as things like the valdotain (?) tress (VT) or distel hitch the prussic cord should be 75% of the rope diameter. For a split tail which is a different animal (ie, not the same as a prussik) where you use blakes or taut line hitch you use the same diameter as the rope.

So 1/2 will work w my 3/4 Samson bull rope? Thanks!

 

[Bango Skank]

Sure, for most friction hitches that’ll probably work. If you just need the hitch to hold tight you could use even smaller. The 2/3 diameter or 2-3mm difference is just to get ideal performance when using a hitch for climbing. I’ve used 8mm cord on 13mm rope and it was a bit grabby and hard to release sometimes, but some fine tuning or a different hitch might’ve fixed it up more.
If a taughtline or Blake’s, you can use the same 3/4”.

What ya doing with that 3/4” and a hitch? Progress capture on mechanical advantage? Lifting?

 

[Howard Justice]

Sure, for most friction hitches that’ll probably work. If you just need the hitch to hold tight you could use even smaller. The 2/3 diameter or 2-3mm difference is just to get ideal performance when using a hitch for climbing. I’ve used 8mm cord on 13mm rope and it was a bit grabby and hard to release sometimes, but some fine tuning or a different hitch might’ve fixed it up more.
If a taughtline or Blake’s, you can use the same 3/4”.

What ya doing with that 3/4” and a hitch? Progress capture on mechanical advantage? Lifting?

Capture for mx advantage pulling trees when masdam not appropriate. We don’t climb. And usually don’t drop em. 95% Storm cleanup - bucking limbing and occ need ropes for rigging for skid access…. if I drop it’s usually on my personal land.